Help me understand the 630 horizontal circuit
 

Specifically, the oscillator and control section.

The chassis I'm wanting to use for my color wheel set has a problem I haven't encountered before, and since the only experience I have is with the synchroguide circuit found in color roundies I figured I would bow to the wisdom of the B&W forum this time.

Issue is I can't get rid of the horizontal blanking bar in the raster, the instructions tell me to adjust the back of the transformer till it goes off the right side of the screen but when I do that the image gets all wavy and I lose sync.

There's a wrinkle: the flyback has a tuning cap on it that shorted out, so I removed it. Is the lack of that capacitor enough to cause a blanking bar in the screen? It's only a 68pf cap.

Can you point to the correct schematic on earlytelevision.org? I don't know anything about the circuit, but would like to follow the discussion.

If I am looking at the right schematic, the horizontal discriminator does not get any feedback back from the flyback, but only from the oscillator. If that's right, eliminating a tuning cap on the flyback or yoke probably changes the retrace speed and high voltage, but not the phasing. Phasing effects would have to come from the discriminator circuit or whatever feeds it.

IIRC, there are also two chassis versions. The Red Book at ARH has two 630 chassis.

http://www.americanradiohistory.com/...ographs-TV.pdf

Last 50 pages of the redbook.

I've never worked on one, dad had one, but swapped it and a VT71 for some test equipment. I do have a 730, courtesy of dad.

Looking at the red book schematic, I see there is a pulse shaping/coupling network between the oscillator and the H discharge (390 pf, 6800 ohms, .01 uF). This could conceivably affect phasing also.

I'm done wild-guessing now.

Have you already modified the set for CBS frame and line rates?

No, I wanted to get it fixed and running at NTSC rates first so I could iron out problems like this. Otherwise if I just skip right to CBS, I'd be chasing my tail on any issues that crop up not knowing whether it's a chassis fault or self induced. I hate that. This black bar is really the only other issue it has, the mods for focus rectifier and shunt regulator work perfectly already. Once I can clear up this issue, I can move on to CBS conversion.

That's why I asked. When modified for CBS rates, you shouldn't have any issues if running properly at NTSC prior to conversion.

Wayne, same basic circuit any 630 has.


http://earlytelevision.org/pdf/rca-630ts-sams-54.pdf


Now that I think of it though, there might not be anything wrong with the oscillator at all. Could it be that the difference in tube size is enough to physically make something like this happen? I mean, the original CRT was a 23CP4 and I have the yoke wrapped around a 10SP4. Could the difference in sweep angles between them make this happen? I'm not sure, I would think the center of a tube is the same no matter what size it is.

The change in tube is going to be an issue for you. The 10SP4 is a ~50 degree tube, the 23CP4 was probably between 70 and 90. (I don't have a datasheet in front of me.)

The degree of deflection experienced by the stream of electrons is governed both the strength of the magnetic field created by the deflection coils and the velocity of the electrons (which is itself governed by final anode voltage accelerating the electrons; we assume the electrons are essentially stationary when at the cathode.)

Whereas the final anode voltages required by 10SP4 and 23CP4 are likely similar, the magnetic field strength required to fully deflect the beam is going to be markedly different for both tubes.

If the 1975 RCA tube manual is correct the 23CP4 crt is a 8 pin keyed button base 110 degree tube. One h--- of a change. 10SP4 again if before said manual is correct is a 50 degree tube. The different h.v. needs could cause diffacuilty. I would go back to the tube that was in set and see what happens,and go from there. All the best, Tom.J

If you turn up the brightness, is there light (raster) in your dark bar, or is the scan width just too small? If it is scanning the blank region, then it's a phasing issue.

Wayne,

I took a shot with the scope triggered on horizontal rate, channel A is the h-drive wave form, channel B is video from the CRT. As you can see the horizontal blanking bar is right is the middle of the drive wave form, which is exactly what I'm seeing on the face of the tube. What I would have expected to see is the blanking bar triggering the end of sweep like it's supposed to, so the blanking bar should roughly line up with the negative going (retrace) portion of the drive wave form.

http://videokarma.org/attachment.php...9&d=1504420916


Since that's not happening, I can only conclude that for some reason the horizontal time base isn't being properly triggered by the horizontal timing pulse. The way things sit at the moment, retrace is being triggered right in the middle of active video and it shouldn't be. No matter what I do with the discriminator transformer it refuses to behave, I can adjust the phase slug to where the bar is nearly off screen but it's very unstable there and the picture gets wavy.

I really don't know what is triggering horizontal prematurely, I can't see anything else that would cause it to happen. Sync pulses coming from the sync section are well defined and have more than enough amplitude, so it's not a sync problem. I don't see any noise with no video present, so that's not it. Next thing I might try is injecting pure horizontal sync pulses to see what will happen, if it behaves like that it might give me a few ideas.

Sweep angle between the 2 CRT's aside, the only issue I was expecting was an overscanned raster horizontally. Vertical is fine, the height pot has enough range to make things work out.

p.243 of the red book (p.9 of the 630TS circuit description) shows the proper waveforms on the plates of the sync discriminator (on the left). Since the horiz is being locked, it must be developing the proper control voltage to the reactance tube, but somehow this is at the wrong phase.

Possibilities I could surmise:

1) The reactance circuit is screwed up and requires an offset input voltage in order to center the frequency (I think not likely, but...).

2) (I think more likely) The transformer that drives the discriminator (which you are tuning) is bad, or tuned way off frequency, or the .015 cap that tunes it is bad, and the discriminator is not being driven by a pure sine wave. I would check the waveforms on the sync discriminator plates to see how they compare to the redbook illustration.

EDIT: redbook p.268 bottom and p.269 top show actual scope waveforms - I see the pulse is much bigger compared to the sine wave than shown in the drawing on p.243, but the phasing is the same.

The circuit in Sams-54 is not a Synchroguide, If the set has the Synchroguide circuit, it is important to align it per the instructions. Typically, you short out the "sinewave" coil, adjust for synch with the hold control centered, then take the short off the sinewave coil and adjust it. The Synchroguide output has a distinct waveform, a sort of hump then dip and spike. The hump should be adjusted (via sinewave coil) to be slightly lower than the spike. The idea was to have a sharper rise time at the end of the waveform for noise immunity (to prevent false triggering). I'll see if I can find an example and post that.

It's not ansynchroguide, I said that in the beginning. I found somewhere that the 630 had a synchro-lock circuit, must be what the synchroguide evolved from.

In any event, I'm going to do what wayne suggests and look at the discriminator. There's got to be a reason why it's acting up, just need to figure it out.

The Redbook (page 265 on the link above) has an extensive procedure for aligning the horizontal. jpg of synchroguide with waveform info attached. "Phasing" is the sinewave coil, the "test points" are there to make it easier to jumper it.

Ok, re-read the original, you were aware it is not synchroguide... And had followed the alignment instructions.. the Redbook also mentions checking R200 and R202 for this problem..

Im very familiar with synchroguide, if that's what this was I wouldn't even be here. What's throwing me off was that reactance tube, but I guess it's not a whole lot different from the later stuff when you think about it. Just a different way of accomplishing the same thing, and the waves look a little different.


Here's what I've been able to find out, so far there are nice sine waves arriving at the 6AL5 and everything looks normal- that is still I put the plate cap back on the HO tube!

Here's h-drive and h-sine with the plate cap removed and no signal input to the chassis, everything looks normal:

http://videokarma.org/attachment.php...6&d=1504478561


And now with the plate cap on:

http://videokarma.org/attachment.php...7&d=1504478561

See that little hump? Apparently the flyback is causing it to show up, so effectively it's self triggering because that pulse has more amplitude than a regular sync pulse does- so any sync pulses from a normal video signal applied to the chassis simple gets drowned out.

I'm still waiting for the flyback tuning capacitor to show up from mouser, so I won't know if the lack of it is what's causing this till it arrives. I really hope that's it, because I'm out of ideas here.

Guys, I'm a little confused here. Nick, you say the original tube is a 23CP4 and you are now using a 10SP4 with the same chassis. The 23CP4 is a 110 deg tube with a 1.125" diameter neck. The 10SP4 is a 50 deg tube with a 1 7/16" dia neck. I don't see how you could get a yoke that was intended for a 23CP4 to accommodate a 10SP4. The yoke for a 23CP4 is just too small in diameter to fit on to the neck of a 10SP4.

Am I missing something here? Also, the sockets are very different between these two CRTs.

I honestly don't remember what it was, could have been a 24CP4 for all I know I gave it away. The yoke is the correct size for a 10" CRT, but I'm going to have to play with the width coil to get the right raster size.

Here are my thoughts, FWIW:
I don't see any explicit connection from the flyback. (correct me if I missed one on the schematic).
Assuming no intentional connection:
Where exactly is that sine wave and spurious pulse? On one of the 6AL5 plates, right? (pin 2 or 7).
Both good and bad waveforms are with nothing attached to antenna input, right? If so, you should try again with a good signal input. See if you get the sync pulse superposed on the sine wave properly then, and check both plates to see if you have same polarity sync and opposite sine wave. Look for the spurious pulse IN ADDITION TO the sync when connecting/disconnecting the HO. Maybe the HO is oscillating back into the tuner. If so, you need to see if the spurious pulse is still there when you have a good signal. If it's still there, that's what you need to chase. But if a normal signal swamps out the spurious pulse, then the bad phasing is still caused by something else.

Wayne,

Yes, the odd pulse appears at the 6AL5, and it's there whenever the flyback is in operation with signal at the antenna or not. What happens with a signal present is that odd signal is triggering the oscillator and the normal sync pulse that should be locking to horizontal just gets taken along for the ride so to speak.

It looks like this one with signal applied:

http://videokarma.org/attachment.php...0&d=1504529857

I don't see how that pulse could get coupled into the phase detector either, since there's no connection present. But that 6AL5 is positioned right below the flyback, so I suppose it's possible the pulse has such a high amplitude its radiating into the circuit and the 6AL5 is the antenna. There's no shield around it surprisingly enough, but I could try adding one to see if it helps matters.

*just noticed the normal sync pulse does indeed have a higher amplitude than the spurious one does, but once horizontal is locked to the spurious pulse there's apparently nothing I can do to get the circuit to 'choose' the correct sync pulse and lock to that. I have to get the spurious pulse out before this thing is going to work properly.*

24CP4 makes sense. It has the same diameter neck and the difference between the deflection angles isn't so great (90 deg vs. 50 deg)

The reason I question the 23CP4 is that was the first CRT I ever replaced in my parents' TV. You don't forget your first.

Is the flyback in the open, or in a cage?

EDIT:
The red book drawing looks like all the H section tubes and the flyback are in a common enclosure.
Does the 6AL5 socket have grounding fingers for a shield?

Nope it doesn't, and honestly I can't see how it ever worked properly without a shield it's just too noisy. I took a 7-pin extension cable and put the 6AL5 far away from the flyback, now it's pretty stable though the h-hold control has a hair trigger. Been watching the Matrix for a half hour now, it hasn't skipped a beat.

http://videokarma.org/attachment.php...8&d=1504560177

http://videokarma.org/attachment.php...9&d=1504560177

Linearity is really good too.

http://videokarma.org/attachment.php...0&d=1504560177

Guess I'll just have to remote mount the 6AL5, I'm satisfied that it will be stable enough come color wheel time. Speaking of which, I'm off to begin building the motor control chassis!

I can't quite stop wondering what's wrong. Does pin 6 of the 6AL5 have a solid ground?

also, is pin 5 a clean, solid -2 volts? The red book shows it connected to a -2 volt supply, I didn't see where it went on the SAMS.

{corrected to say it goes somewhere on both versions}

Everything about the 6AL5 is as it should be, it's just too close to the flyback. Remember that this is not a stock 630, the fly makes more HV and has higher pulses being driven into it (chassis now uses a 6CD6 instead of a 6BG6). I held my scope probe in the same location as the 6AL5, there's a ton of horizontal noise in that area so it's unavoidable that some of it would be coupled into the tube. Even when it's remote mounted it's not perfect, my extension harness isn't shielded so it can be better than it is now.

You may be able to get away with keeping the tube in it's socket, and surrounding the topside of the tube with a shield...

That was the first thing I tried, I'm telling you that tube is so close to the flyback that the only solution is to move it out of the cage. The terminal directly above it carries a 3kv horizontal pulse, so that's probably the one cause the trouble.

:scratch2: I wonder if this is the reason some sets had a 6AL5 mounted under the chassis on it's own little metal bracket , it was picking up some unwanted signal or other ...

No idea, I can only tell you that there’s no way this thing worked properly the way it was. Maybe that’s why the chassis is really low hours and most of the tubes are original, probably didn’t get used much. lol

In any event I was able to source some replacement 3kv capacitors for the flyback, I’ll find out if this odd hump is simply harmonics caused by lack of a tuning capacitor shortly.